Lithographic projection apparatus with positioning system for use with reflectors

ABSTRACT

In a lithographic projection apparatus the positions and/or orientations of reflective optical elements is dynamically controlled. The position of a reflective optical element such as a mirror in an illumination or projection system is first measured using an absolute position sensor mounted on a reference frame and thereafter measured by a relative position sensor also mounted on said reference frame. The position of the element is controlled in accordance with the measured position, e.g. to maintain it stationary in spite of vibrations that might otherwise disturb it. The absolute sensor may be a capacitive or inductive sensor and the relative sensor may be an interferometer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lithographic projection apparatuscomprising:

an illumination system for supplying a projection beam of radiation;

a first object table for holding a mask;

a second object table for holding a substrate;

a projection system for imaging an irradiated portion of the mask onto atarget portion of the substrate.

2. Description of the Related Art

For the sake of simplicity, the projection system may hereinafter bereferred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The illumination system may also include elementsoperating according to any of these principles for directing, shaping orcontrolling the projection beam of radiation, and such elements may alsobe referred to below, collectively or singularly, as a “lens”. Inaddition, the first and second object tables may be referred to as the“mask table” and the “substrate table”, respectively. The mask tableshould be taken as any structure or device that may or does hold anotherstructure or device, generally referred to as a mask, in which a patternto be imaged is or can be formed. Further, the lithographic apparatusmay be of a type having two or more mask tables and/or two or moresubstrate tables. In such “multiple stage” devices the additional tablesmay be used in parallel, or preparatory steps may be carried out on oneor more stages while one or more other stages are being used forexposures.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs). In such a case, the mask(reticle) may contain a circuit pattern corresponding to an individuallayer of the IC, and this pattern can be imaged onto a target area(comprising one or more dies) on a substrate (silicon wafer) which hasbeen coated with a layer of radiation-sensitive material (resist). Ingeneral, a single wafer will contain a whole network of adjacent targetareas which are successively irradiated via the mask, one at a time. Inone type of lithographic projection apparatus, each target area isirradiated by exposing the entire mask pattern onto the target area atonce; such an apparatus is commonly referred to as a wafer stepper. Inan alternative apparatus—which is commonly referred to as astep-and-scan apparatus—each target area is irradiated by progressivelyscanning the mask pattern under the projection beam in a given referencedirection (the “scanning” direction) while synchronously scanning thesubstrate table parallel or anti-parallel to this direction; since, ingeneral, the projection system will have a magnification factor M(generally <1), the speed V at which the substrate table is scanned willbe a factor M times that at which the mask table is scanned. Moreinformation with regard to lithographic devices as here described can begleaned from International Patent Application WO 97/33205.

In general, apparatus of this type contained a single first object(mask) table and a single second object (substrate) table. However,machines are becoming available in which there are at least twoindependently movable substrate tables; see, for example, themulti-stage apparatus described in International Patent Applications WO98/28665 and WO 98/40791. The basic operating principle behind suchmulti-stage apparatus is that, while a first substrate table isunderneath the projection system so as to allow exposure of a firstsubstrate located on that table, a second substrate table can run to aloading position, discharge an exposed substrate, pick up a newsubstrate, perform some initial metrology steps on the new substrate,and then stand by to transfer this new substrate to the exposureposition underneath the projection system as soon as exposure of thefirst substrate is completed, whence the cycle repeats itself; in thismanner, it is possible to achieve a substantially increased machinethroughout, which in turn improves the cost of ownership of the machine.

To reduce the size of features that can be imaged, it is desirable toreduce the wavelength of the illumination beam. To such end, it has beenproposed to use wavelengths of less than about 200 nm, for example 193nm, 157 nm or 126 nm. Further reductions in the wavelength of theillumination radiation, e.g to about 10 to 20 nm, are also envisaged.Such wavelengths in particular are more conveniently focused andcontrolled by reflective optics, such as mirrors. However, mirrors inlithography apparatus must be positioned to especially high accuracy, ascompared to refractive elements, because any rotational orientationerrors are magnified by the total downstream optical path length. In anapparatus using very short wavelength radiation, the optical path lengthmay be of the order of 2 m or more.

For example, to have a good overlay performance, it can be necessary tokeep the position of an image of the irradiated portion of the maskstable at a given position at substrate level with an error (e) of lessthan about 1 nm (see FIG. 3 of the accompanying drawings). If thedistance between the mirror and the substrate (W) is 2 m the maximumpermissible rotational error of the reflected beam, to keep the systemwithin specification, is 28×10⁻⁹ degrees (1×10⁻⁹m/2m=tan 28×10⁻⁹).Since, for a mirror, the angle of reflection equals the angle ofincidence, a rotational error (da) in the position of the mirror willgive rise to twice as large an error in the direction of the reflectedbeam. Thus the mirror must be positioned with an accuracy of 14×10⁻⁹degrees or better. If the mirror has a width of order 0.1 m and arotating point at one side, that rotating point must be positioned towithin 0.024 nm (tan 14×10⁻⁹ ×0.1=2.4×10⁻¹¹). Clearly the accuracy withwhich such a mirror must be orientated is extremely high and will onlyincrease as the specification for image accuracy increases. The accuracyrequirements for position in X, Y and Z are less demanding as sucherrors are magnified less at substrate level.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lithographicprojection apparatus having an improved positioning system to accuratelyand dynamically position a mirror in the radiation or projectionsystems.

According to a first aspect of the present invention, there is provideda lithographic projection apparatus, including:

an illumination system constructed and arranged to supply a projectionbeam of radiation;

a first object table constructed and arranged to hold a mask;

a second object table constructed and arranged to hold a substrate; and

a projection system constructed and arranged to image an irradiatedportion of the mask onto a target portion of the substrate,

wherein at least one of said illumination system and said projectionsystem comprises one or more reflective optical elements and positioningmeans for dynamically controlling a position and/or orientation of oneor more of said reflective optical elements.

The one or more reflective optical elements may comprise a singleelement such as a mirror, a reflective grating, a reflective filter,etc. or a combination of such elements with or without other types ofelement. With the invention, the position of the reflective optics iscontrolled continuously or repeatedly during operation of the apparatusand the effects of vibrations and mechanical shocks, and thermal andmechanical drift thereby can be mitigated.

Preferably, the projection apparatus further comprises sensing meansconstructed and arranged to determine a change in position and/ororientation of one or more of said reflective optical elements, and tooutput one or more position signals indicative thereof; and saidpositioning means comprises:

drive means constructed and arranged to change a position and/ororientation of one or more of said reflective optical elements inresponse to a drive control signal; and

a controller responsive to said one or more position signals forgenerating said drive control signal so as to correct for saiddetermined change in position and/or orientation of one or more of saidreflective optical elements.

In a preferred embodiment of the invention, the lithographic apparatusincludes a reference frame and sensing means for determining theposition of said reflective optics relative to said reference frame.

Also preferably, the sensing means includes:

an absolute position sensing means constructed and arranged to measure aposition and/or orientation of one of said reflective optical elementsand to output an absolute position signal indicative thereof; and

a relative position sensing means constructed and arranged to measurechanges in said position and/or orientation of said one reflectiveoptical element and to output a relative position signal indicativethereof.

Said drive means may be arranged to change said position and/ororientation of said one reflective optical element in response to saiddrive control signal; and said controller may be responsive to saidabsolute and relative position signals for generating said drive controlsignal so as to set and maintain said one reflective optical element ina desired position and/or orientation.

By the use of both absolute position sensing means, which can determinethe absolute position and/or orientation of the reflective opticswithout calibration each time the apparatus is initialized, and relativeposition sensing means, which can detect movements in the positionand/or orientation of the reflective optics with a high bandwidth and/orlarger measuring range, the positioning system can accurately position,or stabilize, the reflective optics without a lengthy calibration orinitialization procedure, and counteract any vibrations in thereflective optics. After an initial position determination using theabsolute sensing means, the drive means are controlled primarily on thebasis of the high frequency output from the relative sensing means orinterferential encoders.

The absolute sensing means preferably include one or more capacitive orinductive sensors and the relative position sensing means preferablyinclude one or more interferometers.

In yet another preferred embodiment said sensing means is constructedand arranged to direct a sensing beam of radiation separate from saidprojection beam along said one or more reflective optical elements; andto determine a position of said sensing beam when having been reflectedby said one or more reflective optical elements.

According to yet a further aspect of the invention there is provided amethod of manufacturing a device using a lithographic projectionapparatus comprising:

an illumination system constructed and arranged to supply a projectionbeam of radiation;

a first object table constructed and arranged to hold a mask;

a second object table constructed and arranged to hold a substrate; and

a projection system constructed and arranged to image an irradiatedportion of the mask onto a target portion of the substrate; the methodcomprising the steps of:

providing a mask bearing a pattern to said first object table;

providing a substrate provided with a radiation-sensitive layer to saidsecond object table;

irradiating portions of the mask and imaging said irradiated portions ofthe mask onto said target portions of said substrate; and

dynamically controlling a position and/or orientation of one or morereflective optical elements comprised in one of said illumination andprojection systems.

In a manufacturing process using a lithographic projection apparatusaccording to the invention a pattern in a mask is imaged onto asubstrate which is at least partially covered by a layer ofradiation-sensitive material (resist). Prior to this imaging step, thesubstrate may undergo various procedures, such as priming, resistcoating and a soft bake. After exposure, the substrate may be subjectedto other procedures, such as a post-exposure bake (PEB), development, ahard bake and measurement/inspection of the imaged features. This arrayof procedures is used as a basis to pattern an individual layer of adevice, e.g. an IC. Such a patterned layer may then undergo variousprocesses such as etching, ion-implantation (doping), metallisation,oxidation, chemo-mechanical polishing, etc., all intended to finish offan individual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4.

Although specific reference may be made in this text to the use of theapparatus according to the invention in the manufacture of ICs, itshould be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered as beingreplaced by the more general terms “mask”, “substrate” and “targetarea”, respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including, forexample, ultraviolet radiation, EUV and X-rays. Also, the terms “mirror”and “reflector” are used synonymously and, unless the context otherwisedetermines, are intended to encompass any reflective element, whetherwholly, partially or selectively reflective and whether or not it hasany other optical, e.g. refractive or diffractive, properties. Where thecontext allows, the term may also apply to non-specular reflectors suchas scatter plates. The term position should be interpreted broadly asreferring to any or all of the X, Y, and Z positions and rotationalpositions Rx, Ry and Rz.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below with reference toexemplary embodiments and the accompanying schematic drawings, in whichlike parts are indicated by like references, and in which:

FIG. 1 depicts a lithographic projection apparatus according to theinvention;

FIG. 2 is a diagram of a positioning system for a mirror according to afirst embodiment of the invention; and

FIG. 3 is a diagram used in explaining the effect of rotational errorsin mirror position on image position at substrate.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

FIG. 1 schematically depicts a lithographic projection apparatusaccording to the invention. The apparatus comprises:

a radiation system LA, IL for supplying a projection beam PB ofradiation (e.g. UV or EUV radiation);

a first object table (mask table) MT provided with a mask holder forholding a mask MA (e.g. a reticle), and connected to first positioningmeans PM for accurately positioning the mask with respect to item PL;

a second object table (substrate table) WT provided with a substrateholder for holding a substrate W (e.g. a resist-coated silicon wafer),and connected to second positioning means PW for accurately positioningthe substrate with respect to item PL;

a projection system (“lens”) PL (e.g. a reflective or catadioptricsystem) for imaging an irradiated portion of the mask MA onto a targetarea, or portion, C of the substrate W.

The radiation system comprises a source LA (e.g. a Hg lamp, an excimerlaser, a laser or discharge plasma source, or an undulator providedaround the path of an electron beam in a storage ring or synchrotron)which produces a beam of radiation. This beam is passed along variousoptical components included in illumination system IL so that theresultant beam PB is collected in such a way as to give a desiredillumination profile at the entrance pupil and the mask.

The beam PB subsequently impinges upon the mask MA which is held in amask holder on a mask table MT. Having been selectively reflected by themask MA, the beam PB passes through the lens PL, which focuses the beamPB onto a target area C of the substrate W. With the aid of theinterferometric displacement measuring means IF and the secondpositioning means PW, the substrate table WT can be moved accurately,e.g. so as to position different target areas C in the path of the beamPB. Similarly, the interferometric displacement measuring means IF andthe first positioning means PM can be used to accurately position themask MA with respect to the path of the beam PB. In general, movement ofthe object tables MT, WT can be realized with the aid of a long-strokemodule (course positioning) and a short stroke module (finepositioning), which are not explicitly depicted in FIG. 1.

The depicted apparatus can be used in two different modes:

1. In step mode, the mask table MT is kept essentially stationary, andan entire mask image is projected in one go (i.e. a single “flash”) ontoa target area C. The substrate table WT is then shifted in the x and/ory directions so that a different target area C can be irradiated by thebeam PB;

2. In scan mode, essentially the same scenario applies, except that agiven target area C is not exposed in a single “flash”. Instead, themask table MT is movable in a given direction (the so-called “scandirection”, e.g. the x direction) with a speed v, so that the projectionbeam PB is caused to scan over a mask image; concurrently, the substratetable WT is simultaneously moved in the same or opposite direction at aspeed V=Mv, in which M is the magnification of the lens PL (typically,M=¼ or ⅕). In this manner, a relatively large target area C can beexposed, without having to compromise on resolution.

Although the present embodiment employs a reflective mask, it will beimmediately appreciated that the present invention may also be used inlithographic apparatus having transmissive masks. The depictedembodiment also employs reflective elements in the radiation andprojections systems, however some refractive elements may also be used.

FIG. 2 illustrates one of the mirrors 10 included in the illuminationoptics IL or projection optics PL and its associated positioning system20, which comprises drive system 30, position sensing system 40 andcontrol system 50. Mirror 10 is depicted for clarity as a flat mirrorset at an acute angle to the incident radiation PB. However, it will beappreciated that mirror 10 may be a glancing incidence mirror and may bemacro- or microscopically shaped to effect any desired shaping orfocusing of the radiation beam PB.

As shown in FIG. 2, mirror 10 is mounted on drives 31, 32 which formpart of the positioning system 30 and which in turn are mounted on baseframe BF. Base frame BF is desirably very solid and may be attached to,or part of, the base plate BP of the lithographic apparatus 1, forexample. Drives 31, 32 are used to accurately control the position, andparticularly the orientation, of the mirror. For clarity, only twodrives are illustrated in FIG. 2 but it will be appreciated that more orfewer drives may be provided to control the position of the mirror inany or all of the six degrees of freedom.

In the present embodiment the drives 31, 32 comprise Lorentz-forcemotors, of which the general working principle, for instance, isdisclosed in European patent application EP 1 001 512 and equivalentU.S. patent application Ser. No. 09/435,638, which are incorporatedherein by reference. Other suitable actuators or motors having a lowstiffness and the necessary responsiveness and power may also beemployed.

The sensing system 40 comprises absolute sensors 41, 42 and relativesensors 43, 44, all of which are mounted on reference frame RF.Reference frame RF is a very stiff frame which is supported by airmounts, springs, or other vibration isolating means and forms thereference for the coordinate system of the apparatus. Reference frame RFmay be part of or connected to reference frames used in other parts ofthe apparatus. It is important that reference frame RF is isolated fromvibrations in the base frame BF, which may be induced, for example, bythe operation of the drives 31, 32.

Absolute sensors 41, 42 measure the absolute position of the mirror 10in one or more degrees of freedom, without the need for calibrationbefore each use. Calibration on initial manufacturing of the apparatusand at periodic maintenance may be necessary or desirable but theabsolute sensors should be able to operate for a fabrication run orseries of runs without calibration. In the present embodiment theabsolute sensors are capacitive sensors or inductive sensors of knowntype. Two absolute sensors are illustrated for the purpose of clarity,but more or fewer may be employed as necessary to provide positioninformation in the desired degrees of freedom.

Relative sensors 43, 44 measure movement, i.e. changes in positionand/or orientation, of the mirror and so would require calibration,involving the mirror being accurately set at a pre-determined position,before being usable to determine the absolute position of the mirror. Inthe present embodiment, relative sensors 43, 44 are interferometer-basedsensors which measure the position of respective reference gratings 45,46 mounted on the mirror 10. As with the absolute sensors, more or fewerthan two sensors may be employed as required.

The interferometer sensors 43, 44 are capable of measuring movements ofthe mirror with a higher sensitivity and/or bandwidth and/or range thanthe capacitive or inductive sensors 41, 42 and therefore are used toprovide continual relative position signals during operation of theapparatus. The absolute sensors 41, 42 are used to provide absoluteposition signals during initial setup of the apparatus and whenre-initializing the apparatus after any period when the projection orillumination systems were not operating. They may also be usedperiodically to verify or recalibrate the interferometer sensors 43, 44.

Raw signals from the absolute sensors 41, 42 and the relative sensors43, 44 are provided to respective first and second signal processingcircuits 51, 52 forming part of the control system 50. The signalprocessing circuits 51, 52 perform appropriate processing andverification of the signals provided by the sensors and transform themas necessary to an appropriate coordinate system for output. Theprocessed position signals from the first signal processing circuit 51,representing the absolute position of the mirror 10, may be provided tothe second signal processing circuit 52 for calibration of the relativeposition signals. A motor control circuit 53 receives the processedposition signals from signal processing circuits 51, 52 and also setpoint data from set point circuit 54 and determines appropriate drivesignals which are provided to motors 31, 32 to position mirror 10 asdesired and counteract the effect of any vibrations.

The control system of the present embodiment uses a feedback controlstrategy based on measuring the position of the mirror and counteractingany deviation from the desired position. The control system may inaddition make use of other sensors or information from the overallcontrol system of the lithographic apparatus to effect a feed-forwardcontrol. The set point provided by set point circuit 54 may be aconstant position if the mirror 10 is a static component of the opticsor may be a variable position if the mirror 10 has a role in anyvariable beam shaping or positioning function of the lithographicapparatus.

Embodiment 2

In a second embodiment of the invention only a position sensing system40 as described for the first embodiment is associated with each of thereflective optical elements, such as mirrors 10, in the projectionoptics PL. Alternative embodiments of the positioning sensing system mayonly comprise absolute or only relative sensors. Changes in positionand/or orientation of the various mirrors can then be monitored duringoperation and an imaginary error at substrate level due to such changescan be derived, since the positions and orientations of the variousmirrors will be known accurately enough for such a derivation.

To correct for the derived imaginary imaging error, one (or more) of themirrors in the projection system is (are) connected to a drive system 30as described for the first embodiment. A control system derives arequired change in the position and/or orientation of its associatedmirror to correct for the various positional and/or rotational errors ofall the mirrors in the projection optics PL as measured by theirassociated positioning sensing systems 40. To this end, raw positionsignals from the various position sensing systems 40 are provided to thecontrol system. Signal processing circuits within the control systemperform appropriate processing of the signals and transform them asnecessary to an appropriate coordinate system for the one (or more)mirror(s) 10 connected to a drive system 30.

One may choose to provide that (those) reflective element(s) with adrive system that are most critical in their position and/or orientationof the reflective elements comprised in the projection system. Further,a position sensing system for that (those) reflective element(s) thatare not critical in their position and orientation may be dispensedwith.

An embodiment alternative to the second embodiment comprises a sensingsystem that provides for a beam of light, preferably a laser beam,passed along the various reflective elements in projection system PLfrom the mask towards the substrate (or vice versa). Positional and/ororientational deviations of the various reflective elements results in achange in position of the laser beam when having passed the projectionsystem, which can be detected using an appropriate two-dimensionaldetector such as a four-quadrant detector (quad cell), a two-dimensionalpositional sensing device or a CCD camera. To provide for a continuousfeedback possibility, the two-dimensional detector can be fixedlymounted on reference frame RF with respect to the projection system andthe laser beam may be reflected from a position on the mask just next toits mask pattern, in which case the two-dimensional detector can bemounted out of the projection beam.

Continuous feedback of positional and rotational deviations of thereflective elements, such as in the first, second and above alternativeembodiment provides for the possibility to correct for position and/orrotation changes in the high, mid and low frequency domain. In case oneonly is interested in deviations and correcting in the low frequencydomain, such as, for instance, induced by mechanical creep of mirrormounts, it is an option to employ a two-dimensional detector mounted onthe substrate table and check the position of the laser beam at selectedinstance in time during an imaging process. A positional error inducedby positional and/or rotational deviations of the reflective elementsmay also be corrected for by accounting for them in the positioning ofthe mask and/or substrate table.

While we have described above specific embodiments of the invention, itwill be appreciated that the invention may be practiced otherwise thandescribed and the description is not intended to limit the invention.The positioning system of the present invention has been described asapplied to a mirror in a lithographic projection apparatus. However, theinvention may also be applied to other components of a lithographicapparatus, such as the substrate (wafer) or mask (reticle) stages, or tocomponents of other apparatus where accurate dynamic positioning isrequired.

What is claimed is:
 1. A lithographic projection apparatus comprising:an illumination system constructed and arranged to supply a projectionbeam of radiation; a first object table constructed and arranged to holda mask; a second object table constructed and arranged to hold asubstrate; and a projection system constructed and arranged to image anirradiated portion of the mask onto a target portion of the substrate;wherein at least one of said illumination system and said projectionsystem comprises a reflective optical element and a positionerconstructed and arranged to control at least one of a position and anorientation of said reflective optical element; wherein said reflectiveoptical element is shaped to effect at least one of shaping and focusingof said beam of radiation.
 2. Apparatus according to claim 1, furthercomprising a sensor constructed and arranged to determine a change in atleast one of a position and an orientation of said reflective opticalelement, and to output a position signal indicative thereof; and whereinsaid positioner includes: an actuator constructed and arranged to changeat least one of a position and an orientation of said reflective opticalelement in response to a drive control signal; and a controllerresponsive to said position signal, said controller configured andarranged to generate said drive control signal.
 3. Apparatus accordingto claim 2, wherein said sensor comprises: an absolute position sensorconstructed and arranged to measure at least one of a position and anorientation of said reflective optical element and to-output an absoluteposition signal indicative thereof; and a relative position sensorconstructed and arranged to measure a change in said at least one of aposition and an orientation of said reflective optical element and tooutput a relative position signal indicative thereof.
 4. Apparatusaccording to claim 3, wherein said controller is responsive to saidabsolute and relative position signals to generate said drive controlsignal.
 5. Apparatus according to claim 3, further comprising areference frame and wherein said sensor is constructed and arranged todetermine at least one of a position and an orientation of saidreflective optical element relative to said reference frame. 6.Apparatus according to claim 5, wherein at least one of said absoluteand relative position sensors comprises a first part mounted on saidreference frame and a second part mounted on said object.
 7. Apparatusaccording to claim 3, wherein said controller is adapted to determine atleast one of an initial position and orientation of said reflectiveoptical element in response to said absolute position signal andthereafter to control at least one of a position and an orientation ofsaid reflective optical element in response to said relative positionsignal.
 8. Apparatus according to claim 3, wherein said relativeposition sensor has a higher measurement bandwidth than said absoluteposition sensor.
 9. Apparatus according to claim 3, wherein saidrelative position sensor has a larger measuring range than said absoluteposition sensor.
 10. Apparatus according to claim 3, wherein saidabsolute position sensor is one of a capacitive and an inductive sensor.11. Apparatus according to claim 3, wherein said relative positionsensor is an interferometric sensor.
 12. Apparatus according to claim 2,wherein said sensor is constructed and arranged to direct a sensing beamof radiation separate from said projection beam along said reflectiveoptical element; and to determine a position of said sensing beam afterreflection by said reflective optical element.
 13. Apparatus accordingto claim 12, further comprising a reference frame wherein said sensor isconstructed and arranged to determine at least one of a position and anorientation of said reflective optical element relative to saidreference frame.
 14. Apparatus according to claim 12, wherein saidsensing beam is a beam of laser radiation.
 15. Apparatus according toclaim 12, wherein said sensor comprises a two-dimensional detectorarranged to determine the position of said sensing beam.
 16. Apparatusaccording to claim 2, wherein said actuator comprises at least oneactuator with low stiffness.
 17. Apparatus according to claim 15,wherein said actuator is a Lorentz-force actuator.
 18. Apparatusaccording to claim 1, wherein said illumination system is adapted tosupply a projection beam of radiation having a wavelength less thanabout 50 nm.
 19. A method of manufacturing a device comprising;providing a mask bearing a pattern to a first object table; providing asubstrate provided with a radiation-sensitive layer to a second objecttable; irradiating portions of the mask and imaging said irradiatedportions of the mask onto target portions of said substrate with aprojection system; and controlling at least one of a position and anorientation of a reflective optical element included in one of anillumination system, supplying a projection beam of radiation and theprojection system; wherein said reflective optical element is shaped toeffect at least one of shaping and focusing of said beam of radiation.20. A device manufactured according to the method of claim
 19. 21. Themethod of claim 19, wherein said controlling of at least one of theposition and an orientation of said reflective optical element isperformed using a linear Lorentz-force actuator.
 22. The method of claim19, wherein said at least one of the position and orientation of saidreflective optical element is controlled in at least two degrees offreedom.
 23. The method of claim 19, wherein said illumination system isadapted to supply a projection beam of radiation having a wavelengthless than about 50 nm.
 24. The method of claim 19, further comprising:determining a change in at least one of a position and orientation ofsaid reflective optical element with respect to a respective desiredstatic position or orientation of said reflective optical element; andchanging said at least one of the position and orientation of saidreflective optical element to correct for said determined change. 25.The method of claim 19, further comprising: determining a change in atleast one of a position and an orientation of said reflective opticalelement; outputting a position signal indicative thereof; changing atleast one of a position and an orientation of said reflective opticalelement in response to a drive control signal; and responsive to saidposition signal, generating said drive control signal.
 26. The method ofclaim 25, further comprising determining at least one of a position andan orientation of said reflective optical element relative to areference frame.
 27. The method of claim 25, wherein said determining achange in said at least one of the position and orientation of saidreflective optical element comprises: measuring at least one of aposition and an orientation of said reflective optical element andoutputting an absolute position signal indicative thereof; and measuringa change in said at least one of the position and orientation of saidreflective optical element and outputting a relative position signalindicative thereof.
 28. The method of claim 27, comprising determiningat least one of an initial position and orientation of said reflectiveoptical element in response to said absolute position signal andthereafter to control at least one of a position and an orientation ofsaid reflective optical element in response to said relative positionsignal.
 29. The method of claim 25, comprising directing a sensing beamof radiation separate from said projection beam along said reflectiveoptical element; and determining a position of said sensing beam afterreflection by said reflective optical element.